Brakes to the floor after changing rear drum cylinders

[FORD*DIEHARD]

'74 , stock 302 with hydroboost front disc/ rear drum setup.

I recently had the Wild Horses front disc brake conversion kit installed in March. Have not had any problems...... until yesterday when I changed out the rear drum cylinders. Everything went back together smooth. When I bleed the back pumping a couple times very little came out but when I check the reservoir it was empty. Obviously added more fluid, continued to bleed the entire system several times but still when I turn her on the pedal goes to the floor. Tried bleeding more, minimal amount of fluid coming out.

Am I missing something? Are you supposed to bleed the system with the vehicle on with hydroboost?

I double checked the rear drums adjustment and those were good.

Thank you in advance for your time/help,

Sonny

 

[Bitch'nBronco]

I'd try gravity bleeding it, its likely that theres still a significant air bubble in the lines since you emptied the res. I had a similar problem years ago, and wound up taking it to a shop to vacuum bleed it. Another option would be to vacuum bleed. Shouldn't need to have the engine running

 

[B RON CO]

Hi, I agree to gravity bleed the wheels, one at a time, longest line to shortest line. You may have to pump the pedal every now and then while the bleeders are closed. After the fluid trickles out of each wheel go back to the vacuum bleeding. And now you know, don't let the master cylinder go empty. That probably caused all the trouble. Good luck

 

[FORD*DIEHARD]

So I was told that if I pump the pedal with the engine off and pressure builds up the possible issue is an air bubble in the master cylinder and the only way of eliminating that air bubble would be to bench bleed the master cylinder again.

I was looking up what was suggested and ran across this video (

) a place using a syringe to (bleed the master cylinder). Using a bleeder kit the had the lines running back into the master cylinder and used the syringe to force fluid through the master cylinder. They had it on the bench but it seems like this would be possible to accomplish this with the master cylinder on the Bronco.

Has anyone done it this way before? Was it successful or was it more work than just pulling the master cylinder back off and actually bench bleed it again?

Thank you in advance for your time/help,

Sonny

 

[DirtDonk]

I’m not sure how much a legitimate test that is with a power-assist brake system.
With the engine off you can hardly push the pedal down to begin with. Fluid or no fluid. Whether vacuum booster or hydroboost.
Have you done this already and what does the pedal feel like? With the engine off is the pedal hard as a rock after one or two pumps?
If so that’s probably just a booster acting normal I would think.

 

[fluffybunny]

When I bench bled mine, it used this. https://www.amazon.com/dp/B002JSM7HA/?tag=cbama-20. It worked as it should but you have to apply quite a bit of pressure on the syringe against the master cylinder to prevent fluid from squirting out around the edge of the master cylinder fitting.

 

[Apogee]

You probably just have a big 'ol air bubble in the rear brake circuit, or you may have failed the master cylinder during bleeding, but if you replaced that in March as well with the front disc brake conversion kit, that would be unlikely. I would personally let it gravity bleed for a while until I could get a good stream of fluid at each caliper with a 2-person bleed, and then bleed normally.

Alternatively, if you do think there's air trapped in the MC seals, I would do a plugged-port bleed on the rear brake circuit only while it's on the EB until I had a good, high, firm pedal, and then I'd reconnect the line, bleed the fitting at the MC a few times into a rag with someone else pumping the pedal, and then working fluid back to the rear corners.

Tobin

 

[FORD*DIEHARD]

I'm going to try the plunged port tomorrow. Just making sure is there anything that you can mess up doing this? If there is , what do I need to do to avoid jacking anything up and setting me back even further?

Thank you in advance for your time/help,

Sonny

 

[gnpenning]

Back in the day when I had a tough one to bleed, after bench bleeding and trying to regular bled and gravity bleeding. I would open the farthest away bleeder and have a helper quickly push the pedal to the floor, close bleeder and repeat a couple times. The concept is to push the air bubble out with the rush of fluid or at least move it closer to the bleeder. Never had it fail. You may have to do both sides.